1. Field of the Invention
The present invention relates to optical devices, and optical apparatuses provided therewith, specifically to optical devices capable of producing light of a micro spot size, for example, such as near-field light, and optical apparatuses provided with such optical devices.
2. Description of the Related Art
Various techniques that use light of a micro spot size, for example, such as near-field light, as recording light have been proposed to realize high-density recording in an information recording medium. Because the use of near-field light realizes a micro light spot that exceeds the diffraction limit of light, for example, a thermal assist magnetic recording technique that uses near-field light has gained attention as a promising technique for the next-generation high-density magnetic recording. Further, various techniques that use near-field light for an information recording medium that uses a magneto-optical recording film or a phase-change recording film have been studied.
In this connection, various types of optical devices that produce light of a micro spot size, for example, such as near-field light, have been proposed (see, for example, Japanese Patent No. 3956939, Patent Document 1; and JP-A-2009-26360, Patent Document 2).
Patent Document 1 proposes an optical device that includes an optical device main body, and a conductive film formed on a surface of the optical device main body. A circular aperture is formed at the center of the conductive film. In the optical device disclosed in this publication, light is shone on the conductive film through the optical device main body to produce surface plasmons at the aperture edge of the conductive film, and light of a micro spot size substantially equal to the size of the circular aperture is emitted through the circular aperture.
Further, in Patent Document 1, periodic indentations are formed on the surface of the conductive film on the side of the optical device main body, and the surface plasmon enhancement effect produced by the indentations is utilized to improve the transmission efficiency through the circular aperture. Further, Patent Document 1 specifies the relationship between the beam size of the incident light and the periodic structure of the conductive film surface to improve the transmission efficiency through the circular aperture of the conductive film. Patent Document 1 also proposes an optical head and an optical recording and reproducing apparatus that include an optical device of the configuration described above.
Patent Document 2 proposes an optical device of a configuration similar to that described in Patent Document 1. In Patent Document 2, in order to improve transmission efficiency through the circular aperture of the conductive film, the aperture size is varied stepwise along the axial direction of the circular aperture so as to minimize the size of the circular aperture in the vicinity of the portion from which the light emerges.
Further, a technique has been proposed concerning a photodiode that is configured using an optical device that utilizes the surface plasmon enhancement effect (see, for example, Tsutomu Ishi et al.: Si Nano-Photodiode with a Surface Plasmon Antenna, JJAP vol. 44, No. 12, 2005, pp. L364-L366, Non-Patent Document 1).